In the prior art, it is known for example from DE 102013111110 A1 that engines with exhaust-gas recirculation systems can be configured to divert at least a part of the exhaust gas from an engine outlet passage to an engine intake passage. Engine pumping work and NOx emissions can be reduced by means of exhaust-gas recirculation (EGR). For example, for the same engine load, the throttle may be controlled to open to a greater extent during exhaust gas recirculation than the extent to which the throttle may be controlled open when exhaust gas recirculation is not occurring. Pumping losses can be reduced by reducing the throttling of the engine, which improves the fuel efficiency. Furthermore, with exhaust-gas recirculation, the combustion temperature can be reduced, which reduces an amount of NOx generated during the combustion.
The present disclosure is based on the object of making it possible for parameters for an exhaust-gas after-treatment device to be influenced more easily, and thus for the exhaust-gas after-treatment device to be controlled more effectively.
In one example, a motor vehicle having a hybrid drivetrain comprises an electric machine and an internal combustion engine, an intake-air tract, an exhaust tract, an exhaust-gas after-treatment device which is arranged in the exhaust tract, and an exhaust-gas recirculation tract which is designed to conduct exhaust gas out of the exhaust tract from an exhaust-gas extraction point, arranged downstream of the exhaust-gas after-treatment device, to an exhaust-gas introduction point, arranged in the intake-air tract, as a result of which a loop is formed. In order to check whether a corrective measure should be taken to ensure effective functioning of the exhaust-gas after-treatment device, at least one value which characterizes a current state of an exhaust-gas after-treatment device is compared with a setpoint value of the exhaust-gas after-treatment device. If, in the event of a deviation of the value which characterizes the current state of the exhaust-gas after-treatment device from the setpoint value, a demand for a measure (such as a corrective measure) is detected, and the measure is implemented in a measure implementation step. The measure here comprises supplying an intake charge (alternately referred to herein as “charge gas”), which has recirculated exhaust gas, to the internal combustion engine during overrun operation. In particular, charge gas which is formed entirely from recirculated exhaust gas is fed to the engine.
The exhaust-gas after-treatment actual value is detected in an exhaust-gas after-treatment value detection step. The exhaust-gas after-treatment actual value can be based on at least one measured value or else on a result of a mathematical model. The measure is, in particular, a measure for reducing nitrogen oxides (NOx).
The operating conditions of the at least one exhaust-gas after-treatment device are advantageously influenced by means of the operating method. The desired influencing is implemented here either directly during the operating method in the overrun operation, or immediately after the internal combustion engine has returned from overrun operation. During overrun conditions the internal combustion engine may not provide torque for operating the vehicle and the throttle may be maintained in closed position. The exhaust-gas after-treatment device is kept within predefined parameters or is adjusted to said parameters in which the exhaust-gas after-treatment device functions optimally. As a result, the effectiveness of the exhaust-gas after-treatment device is increased and undesired emissions are reduced.
In particular, the temperature of the exhaust-gas after-treatment device is influenced by means of the flushing of the exhaust-gas after-treatment device with recirculated exhaust gas during overrun operation of the internal combustion engine. In addition to the exhaust gas recirculation, the measure can comprise introducing fuel into the loop (that is to say into the internal combustion engine or into the exhaust tract).
The exhaust-gas composition can advantageously be influenced by introducing the fuel during the measure. Richer exhaust gas can be generated. In the exhaust-gas after-treatment device, configured as a nitrogen oxide storage catalytic converter, the richer exhaust gas can bring about a release of the stored nitrogen oxides which can then be converted in a second exhaust-gas after-treatment device, embodied as a selectively active reduction catalytic converter. Here, the fuel may be introduced, in particular in a post-injection, into a combustion chamber of the internal combustion engine or into the exhaust tract, in particular upstream of the exhaust-gas after-treatment device. Also, reduction of trapped nitrogen oxides (NOx) can be brought about by additionally feeding in urea solution (urea), which reacts in the exhaust gas to form ammonia (NH3). Instead of the urea solution, it is also possible for some other substance to be introduced which makes a reducing agent available in the SCR catalytic converter or is itself a reducing agent, in particular ammonia.
In one advantageous embodiment of the operating method according to the disclosure, the measure comprises operating the electric machine. The electric machine can be operated in such a way that the electric machine drives the motor vehicle, or else in such a way that the internal combustion engine reaches or maintains a specific rotational speed. In particular, the internal combustion engine may be kept constant at a predefined rotational speed during the measure.
In this way, the hybrid drivetrain is used to decouple the internal combustion engine from the drive during the measure. The internal combustion engine can, as a result, be used solely for influencing the exhaust-gas after-treatment devices arranged in the loop. The internal combustion engine can stay in the overrun operation by virtue of the motor vehicle being driven by means of the electric machine. The phases of the overrun operation of the internal combustion engine can therefore be extended. The operating state of the internal combustion engine becomes less dependent on the driving state of the motor vehicle. By driving the internal combustion engine by means of the electric machine, the internal combustion engine can, in overrun operation, reach any desired rotational speed which is independent of the current motor vehicle speed. The mass flow through the internal combustion engine can as a result be optimized for the measure, and the measure can be carried out more effectively. Moreover, a constant rotational speed of the internal combustion engine makes the measure easier to control.
In the demand check, consideration is given, in particular, to ammonia loading in the exhaust-gas after-treatment device, embodied as a selectively active reduction catalytic converter. The measure is carried out if the detected exhaust-gas after-treatment actual value for the ammonia loading falls below the exhaust-gas after-treatment setpoint value for the ammonia loading.
This advantageously ensures that a predefined quantity of ammonia, which is available for the reduction of the nitrogen oxides, is stored in the exhaust-gas after-treatment device, embodied as a selectively active reduction catalytic converter. The measure can be carried out as a function of the ammonia which is already present.
As an alternative to or in addition, in the demand check, consideration is given to a nitrogen oxide load in the exhaust-gas after-treatment device, embodied as a nitrogen oxide storage catalytic converter. The measure is carried out if the detected exhaust-gas after-treatment actual value for the nitrogen oxide load exceeds the exhaust-gas after-treatment setpoint value for the nitrogen oxide load.
This advantageously ensures that, when there is a predefined quantity of nitrogen oxides which are stored in the exhaust-gas after-treatment device, embodied as a nitrogen oxide storage catalytic converter, a measure for reducing them may be carried out. The exhaust-gas after-treatment device is therefore operated within the limits of its capacity. The measure can be carried out as a function of the capacity utilization of the exhaust-gas after-treatment device.
As an alternative to or in addition, in the demand check, consideration is given to a nitrogen oxide content upstream of the exhaust-gas after-treatment device, embodied as selectively active reduction catalytic converter. The measure is carried out if the detected exhaust-gas after-treatment actual value for the nitrogen oxide content exceeds the exhaust-gas after-treatment setpoint value for the nitrogen oxide content.
As a result it is detected if a nitrogen oxide storage catalytic converter arranged upstream of the selectively active reduction catalytic converter no longer absorbs nitrogen oxides to a desired amount. The measure can also be carried out here as a function of the capacity utilization of the exhaust-gas after-treatment device.
The demand check in the operating method takes place in such a way that not only a deviation of the exhaust-gas after-treatment actual value from the exhaust-gas after-treatment setpoint value is determined, but also the difference that is currently present between the exhaust-gas after-treatment actual value and the exhaust-gas after-treatment setpoint value is also determined. An extent of the required measure can be determined therefrom. The demand check is therefore carried out at the beginning of the operating method, at the moment when the exhaust-gas recirculation valves open. In particular, a time period for the measure to be carried out can be determined. As a result, the performance of the measure can be adjusted as a function of the extent of deviation of the current after-treatment value from the setpoint value.
In a further embodiment of the operating method according to the disclosure, in a motor vehicle value detection step, at least one motor vehicle actual value, which characterizes a current motor vehicle actual state, is detected, and in a capability check, said motor vehicle actual value is compared with at least one motor vehicle setpoint value, and the measure is implemented under the condition that the capability of the motor vehicle to implement the measure is identified if the motor vehicle actual value corresponds to the motor vehicle setpoint value. In the capability check, in particular, consideration is given to a hybrid drivetrain value or a motor vehicle speed or an engine speed or a motor vehicle load or a fuel injection quantity or a brake pedal position or an accelerator pedal position or a clutch pedal position or an item of navigation information or an item of traffic information or an item of cruise control system information.
As a result, consideration is also given to the current state of the motor vehicle, and it can be determined whether it is at all possible for the desired conditions to be brought about, or whether it is likely that said desired conditions will be brought about, in said current state.
The motor vehicle according to another example of the disclosure comprises a hybrid drivetrain having an electric machine and an internal combustion engine, an intake-air tract, an exhaust tract, an exhaust-gas after-treatment device arranged in the exhaust tract, and an exhaust-gas recirculation tract which is designed for conducting exhaust gas out of the exhaust tract from an exhaust-gas extraction point arranged downstream of the exhaust-gas after-treatment device to an exhaust-gas introduction point arranged in the intake-air tract, as a result of which a loop is formed. The motor vehicle has at least one valve, an exhaust-gas after-treatment value detection unit for detecting an exhaust-gas after-treatment actual value, and a control unit which is designed to identify overrun operation of the internal combustion engine and to adjust the at least one valve during overrun operation in such a way that charge gas, which has recirculated exhaust gas, can be fed to the internal combustion engine, and which is designed to control the electric machine.
The motor vehicle has, in particular, a first exhaust-gas after-treatment device arranged in the exhaust tract, and a second exhaust-gas after-treatment device arranged downstream of the first exhaust-gas after-treatment device and upstream of the exhaust-gas extraction point. The first exhaust-gas after-treatment device is, in particular, a nitrogen oxide storage catalytic converter, and the second exhaust-gas after-treatment device is, in particular, a selectively active reduction catalytic converter which can be a Selective Catalytic Reduction (SCR) catalytic converter (or a particle filter with SCR coating (SCRF for SCR on filter). Both low-pressure and high-pressure EGR may be provided. The hybrid drivetrain can be a parallel or serial hybrid drivetrain.
A motor vehicle with a hybrid drivetrain is therefore provided which makes it possible to perform exhaust-gas recirculation during overrun operation of the internal combustion engine. This therefore makes it possible to influence the operating parameters of the exhaust-gas after-treatment devices arranged in the loop. The hybrid drivetrain also makes it possible to decouple the internal combustion engine from the driving operation (providing torque), at least for a specific time period, and to use said internal combustion engine solely for the measure of influencing the exhaust-gas after-treatment device.
In one embodiment, the motor vehicle has a fuel injector which is designed to introduce fuel into the loop, the control unit being designed to control the fuel injector. The fuel injector is designed, in particular, to introduce the fuel into a combustion chamber of the internal combustion engine or into the exhaust tract.
It is therefore made possible for the exhaust-gas recirculation to be combined with an injection of fuel, and for the composition of the exhaust-gas flow to be influenced even during overrun operation of the internal combustion engine. Increasing the proportion of fuel makes it possible to generate richer exhaust gas, which is advantageous, for example, for regenerating the nitrogen oxide storage catalytic converter.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.